Florey Department of Neuroscience and Mental Health - Research Publications
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ItemClozapine regulation of p90RSK and c-Fos signaling via the ErbB1-ERK pathway is distinct from olanzapine and haloperidol in mouse cortex and striatum(PERGAMON-ELSEVIER SCIENCE LTD, 2013-01-10)Treatment of the positive psychotic symptoms of schizophrenia with standard antipsychotic drugs (APDs) is ineffective in a proportion of cases. For these treatment resistant patients the alternative is the APD clozapine which is superior to other agents but carries serious side effects. Why clozapine is uniquely effective is unknown, but we have previously postulated may involve G-protein coupled receptor (GPCR) and epidermal growth factor (EGF) receptor (ErbB1) transactivation signaling to the mitogen-activated protein kinase-extracellular signal regulated kinase (MAPK-ERK) cascade. This was based upon clozapine induced initial down-regulation and delayed ErbB1 mediated activation of the cortical and striatal ERK response in vivo distinct from other APDs. This study investigated if modulation of the ErbB1-ERK1/2 pathway by clozapine, olanzapine and haloperidol affected expression of the ERK substrates p90RSK and c-Fos, factors that regulate transcription of proteins associated with neuroplasticity and synapse formation in C57Bl/6 mice. In cortex and striatum, acute clozapine treatment induced biphasic p90RSK phosphorylation via MEK that paralleled ERK phosphorylation independent of EGF receptor blockade. By contrast, olanzapine and haloperidol caused p90RSK phosphorylation that was not concomitant with ERK signaling over a 24-hour period. For c-Fos, clozapine elevated expression 24h after administration, a timeframe consistent with ERK activation at 8h. Alternatively, haloperidol stimulation of c-Fos levels limited to the striatum was in accord with direct transcriptional regulation through ERK. The unique spatio-temporal expression of downstream nuclear markers of the ErbB1-ERK pathway invoked by clozapine may contribute to its effectiveness in treatment resistant schizophrenia.
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ItemClozapine induction of ERK1/2 cell signalling via the EGF receptor in mouse prefrontal cortex and striatum is distinct from other antipsychotic drugs(CAMBRIDGE UNIV PRESS, 2012-09-01)Treatment resistance remains a major obstacle in schizophrenia, with antipsychotic drugs (APDs) being ineffective in about one third of cases. Poor response to standard therapy leaves the APD clozapine as the only effective treatment for many patients. The reason for the superior efficacy of clozapine is unknown, but as we have proposed previously it may involve modulation of neuroplasticity and connectivity through induction of interconnected mitogenic signalling pathways. These include the mitogen-activated protein kinase-extracellular signal regulated kinase (MAPK-ERK) cascade and epidermal growth factor (EGF)/ErbB systems. Clozapine, distinct from other APDs, induced initial inhibition and subsequent activation of the ERK response in prefrontal cortical (PFC) neurons in vitro and in vivo, an action mediated by the EGF receptor (ErbB1). Here we examine additionally the striatum of C57Bl/6 mice to determine if clozapine, olanzapine, and haloperidol differentially regulate the ERK1/2 pathway in a region or time-specific manner conditional on the EGF receptor. Following acute treatment, only clozapine caused delayed striatal ERK phosphorylation through EGF receptor phosphorylation (tyrosine 1068 site) and MEK that paralleled cortical ERK phosphorylation. Olanzapine induced initial pERK1-specific blockade and an elevation 24-h later in PFC but had no effect in the striatum. By contrast, haloperidol significantly stimulated pERK1 in striatum for up to 8 h, but exerted limited effect in PFC. Clozapine but not olanzapine or haloperidol recruited the EGF receptor to signal to ERK. These in-vivo data reinforce our previous findings that clozapine's action may be uniquely linked to the EGF signalling system, potentially contributing to its distinctive clinical profile.
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ItemQuetiapine and aripiprazole signal differently to ERK, p90RSK and c-Fos in mouse frontal cortex and striatum: role of the EGF receptor(BIOMED CENTRAL LTD, 2014-02-20)BACKGROUND: Signaling pathways outside dopamine D2 receptor antagonism may govern the variable clinical profile of antipsychotic drugs (APD) in schizophrenia. One postulated mechanism causal to APD action may regulate synaptic plasticity and neuronal connectivity via the extracellular signal-regulated kinase (ERK) cascade that links G-protein coupled receptors (GPCR) and ErbB growth factor signaling, systems disturbed in schizophrenia. This was based upon our finding that the low D2 receptor affinity APD clozapine induced initial down-regulation and delayed epidermal growth factor receptor (EGFR or ErbB1) mediated activation of the cortical and striatal ERK response in vivo distinct from olanzapine or haloperidol. Here we map whether the second generation atypical APDs aripiprazole and quetiapine affect the EGFR-ERK pathway and its substrates p90RSK and c-Fos in mouse brain, given their divergent agonist and antagonist properties on dopaminergic transmission, respectively. RESULTS: In prefrontal cortex, aripiprazole triggered triphasic ERK phosphorylation that was EGFR-independent but had no significant effect in striatum. Conversely quetiapine did not alter cortical ERK signaling but elevated striatal ERK levels in an EGFR-dependent manner. Induction of ERK by aripiprazole did not affect p90RSK signaling but quetiapine decreased RSK phosphorylation within 1-hour of administration. The transcription factor c-Fos by comparison was a direct target of ERK phosphorylation induced by aripiprazole in cortex and quetiapine in striatum with protein levels in temporal alignment with that of ERK. CONCLUSIONS: These data indicate that aripiprazole and quetiapine signal to specific nuclear targets of ERK, which for quetiapine occurs via an EGFR-linked mechanism, possibly indicating involvement of this system in its action.